With respect to so-called metallic inks and metallic coating materials containing flake pigments of aluminum, copper and their alloys, various kinds of resins are used as a binder and in recent years, so-called UV metallic inks and UV metallic coating materials using ultraviolet curable resins advantageous in the quick curability, low-pollution, and energy saving property have been investigated. However the metals, which are the flake pigments, in the UV metallic inks and UV metallic coating materials promote the initiation of polymerization of the monomers or oligomers existing in the ultraviolet curable resins, so that there occurs a problem that gelation of the inks and coating materials occurs within a short time during the storage period. Further, articles printed or coated by the inks and coating materials tend to lose the metallic luster of the ink films and the coating films owing to the oxidation of the metal flakes with the lapse of time.
To solve such problems, Patent Document No. 1 discloses a metal powder-containing active beam-curable ink obtained by adding a nitrocellulose with a low polymerization degree to an active energy beam-curable ink containing a metal powder.
However, the method requires to increase the addition amount of the nitrocellulose to be added so as to achieve a satisfactory result in terms of the number of days taken until gelation of the inks and coating materials and therefore, the viscosity of the inks and coating materials tends to increase and the adhesion property of ink films or coating films tends to be deteriorated. Further, in order to assure the uniform dispersion of the nitrocellulose in the inks and coating materials, the stirring duration at the time of ink and coating material production is so prolonged that an excess shear force is applied to the metal flakes and subsequently deterioration of the metallic effect may possibly be deteriorated owing to deformation of the flakes themselves. Further, with respect to deterioration of the stability with the lapse of time and metallic luster of the ink films or coating films, even if the nitrocellulose is added more, the effect of the increase of addition to improve these properties is limited.
Patent Document No. 1: Japanese Patent Laying-Open No. 2002-249697